JP3550978B2 - Control device for electric power steering device - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a control device of an electric power steering device that applies a steering assisting force by a motor to a steering system of an automobile or a vehicle, and particularly to reliably detect a failure of the motor drive system and stop driving the motor. To a control device for an electric power steering device.
[0002]
[Prior art]
2. Description of the Related Art An electric power steering device that urges a steering device of an automobile or a vehicle with an auxiliary load by a rotating force of a motor applies an auxiliary load to a steering shaft or a rack shaft by a transmission mechanism such as a gear or a belt through a reduction gear. It is designed to be energized.
[0003]
FIG. 7 shows a configuration of a general electric power steering device. A shaft 2 of a steering handle 1 is connected to a tie rod 6 of a steered wheel via a reduction gear 3, universal joints 4a and 4b, and a pinion rack mechanism 5. ing. The shaft 2 is provided with a torque sensor 10 for detecting a steering torque of the steering wheel 1. A motor 20 for assisting the steering force of the steering wheel 1 is coupled to the shaft 2 via a clutch 21 and a reduction gear 3. Have been. Power is supplied from a battery 14 to a control unit 30 that controls the power steering device via an ignition key 11. The control unit 30 controls the steering torque T detected by the torque sensor 10 and the vehicle speed V detected by the vehicle speed sensor 12. , The steering assist command value I of the assist command is calculated, and the current supplied to the motor 20 is controlled based on the calculated steering assist command value I. The clutch 21 is ON / OFF controlled by the control unit 30, and is ON (coupled) in a normal operation state. The clutch 21 is turned off (disengaged) when the control unit 30 determines that the power steering device is out of order and when the power of the battery 14 is turned off by the ignition key 11.
[0004]
Although the control unit 30 is mainly composed of a CPU, a general function executed by a program inside the CPU is as shown in FIG. For example, the phase compensator 31 does not indicate a phase compensator as independent hardware, but indicates a phase compensation function executed by the CPU. Incidentally, the control unit 30 may not be constituted by the CPU, but each functional element may be constituted by independent hardware.
[0005]
Here, general functions and operations of the control unit 30 will be described. The steering torque T detected and input by the torque sensor 10 is phase-compensated by a phase compensator 31 in order to enhance the stability of the steering system, and the phase-compensated steering torque TA is input to a steering assist command value calculator 32. Is done. The vehicle speed V detected by the vehicle speed sensor 12 is also input to the steering assist command value calculator 32. The steering assist command value calculator 32 determines a steering assist command value I that is a control target value of the current supplied to the motor 20 based on the input steering torque TA and the vehicle speed V. Is provided with a memory 33. The memory 33 stores a steering assist command value I corresponding to the steering torque using the vehicle speed V as a parameter, and is used for calculating the steering assist command value I by the steering assist command value calculator 32. The steering assist command value (motor current command value) I is input to a subtractor 30A, and is also input to a feedforward differential compensator 34 for increasing the response speed, and the deviation (I-i) of the subtractor 30A is The proportional output is input to the proportional calculator 35, and the proportional output is input to the adder 30B and also to the integration calculator 36 for improving the characteristics of the feedback system. The outputs of the differential compensator 34 and the integration compensator 36 are also added to the adder 30B, and the current control value E, which is the result of the addition in the adder 30B, is input to the motor drive circuit 37 as a motor drive signal. The motor current detection value i of the motor 20 is detected by the motor current detection circuit 38, and the motor current detection value i is input to the subtractor 30A and fed back.
[0006]
An example of the configuration of the motor drive circuit 37 will be described with reference to FIG. 9. The motor drive circuit 37 drives the respective gates of the field effect transistors (FETs) FET1 to FET4 based on the current control value E from the adder 30B. It comprises a drive circuit 371, an H bridge circuit composed of FET1 to FET4, a boost power supply 372 for driving the high side of FET1 and FET2, and the like. FET1 and FET2 are turned on / off by a PWM (pulse width modulation) signal having a duty ratio D1 determined based on the current control value E, and the magnitude of the current Ir actually flowing to the motor is controlled. The FET 3 and the FET 4 are driven by a PWM signal having a duty ratio D2 defined by a predetermined linear function (D2 = a · D1 + b, where a and b are constants) in a region where the duty ratio D1 is small, and a region where the duty ratio D1 is large. Is turned on / off according to the rotation direction of the motor determined by the sign of the PWM signal. For example, when the FET 3 is in a conductive state, a current flows through the FET 1, the motor 20, the FET 3, and the resistor R1, and a positive current flows through the motor 20. When the FET 4 is in the conductive state, the current flows through the FET 2, the motor 20, the FET 4, and the resistor R2, and a negative current flows through the motor 20. Therefore, the current control value E from the adder 30B is also a PWM output. Further, the motor current detection circuit 38 detects the magnitude of the forward current based on the voltage drop across the resistor R1, and detects the magnitude of the negative current based on the voltage drop across the resistor R2. The motor current detection value i detected by the motor current detection circuit 38 is input to the subtractor 30A and fed back.
[0007]
In such a configuration, when a disconnection failure occurs between the motor 20 and the control unit 30 or when the FET or its drive circuit fails, the motor drive signal is output from the motor drive circuit 37. Regardless, no current flows through the motor 20, and the assist force by the motor 20 cannot be generated. For this reason, the steering feels heavy at low speeds or when the vehicle is stationary, and it is necessary to notify the driver of the abnormality by displaying a warning. Further, if the motor current detection circuit 38 fails, the motor current detection value i cannot be detected, so that an excessive current is supplied to the motor, the assist becomes excessive, and the steering becomes unstable. When the motor line is grounded, almost no current flows through the motor current detection circuit 38, so that the current is further attempted to flow to the motor by feedback control.
[0008]
[Problems to be solved by the invention]
Conventionally, when detecting a failure in the motor drive system as described above, a motor current command value and a detected motor current value are compared, and if the difference is equal to or greater than a predetermined value, it is determined that the failure has occurred. FIG. 10 shows the configuration in correspondence with FIG. 8. The abnormality detection unit 39 includes a steering assist command value I from the steering assist command value calculator 32 and a motor current detection value i from the motor current detection circuit 38. When the difference is equal to or greater than a predetermined threshold, an abnormal signal AL is output, and the motor drive circuit 37 stops driving the motor 20.
[0009]
However, a counter electromotive force is generated in the motor 20 when the steering wheel is returned or when the steering wheel is suddenly steered, and the current may cause the motor current detection value i to become smaller than the normal value. In such a case, the above detection method has erroneously detected a failure in the motor drive system. Conventionally, detection conditions (detection time, detection value) have been adjusted to prevent such erroneous detection, but conversely, failures cannot be reliably detected.
[0010]
The present invention has been made in view of the circumstances described above, and an object of the present invention is to provide a control device for an electric power steering device that reliably detects a failure in a motor drive system and stops the motor drive. It is in.
[0011]
[Means for Solving the Problems]
The present invention provides a torque sensor that detects a steering torque of a steering wheel, a motor that applies an auxiliary load to a steering shaft that is provided integrally with the steering wheel, and a control that drives the motor according to the magnitude of the steering torque. relates controller of an electric power steering apparatus having a unit, the object of the present invention, the motor current detection value is below a predetermined value, the integrated value of the motor terminal voltage or PWM duty ratio is larger than a predetermined value Is continued for a predetermined time, this is achieved by determining that the motor drive system has failed and stopping the drive of the motor.
[0012]
Further, when the motor current detection value is equal to or less than a predetermined value and the output of the integrator of the control unit is equal to or more than a predetermined value for a predetermined time, it is determined that the motor driving system has failed and the driving of the motor is stopped. Is achieved by letting
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
The value of the current flowing through the motor of the power steering device is controlled to be constant by feedback control (for example, PI control) based on the motor current command value and the detected motor current value as described above. Then, for example, when a disconnection fault occurs between the motor and the control unit, the motor current detection value is zero despite the application of the motor current command value. It increases sharply and reaches a maximum. Therefore, the output of the integrator that integrates the motor terminal voltage or the value of the PWM duty ratio, or the output of the integrator of the PI controller is monitored, and the integrated value of the duty ratio assumed from the current command value in a normal state is monitored. If the state in which the difference is large continues for a predetermined time, it can be determined that the motor drive system is abnormal. Similarly, when the motor current cannot be detected for other faults, that is, when the detected motor current value is zero, the voltage between the motor terminals or the PWM duty ratio is rapidly increased by the feedback control. In this case, it can be determined that a failure has occurred when the predetermined time has elapsed.
[0014]
The comparison between the motor terminal voltage and the integrated value of the duty ratio may be performed based on the current detection value instead of the current command value. Further, when the battery voltage fluctuates or the motor resistance changes due to temperature change, the duty ratio of the PWM to the motor current command value changes. Therefore, the detected value is corrected by the battery voltage or the motor resistance value. This makes it possible to more reliably detect an abnormality in the motor drive system.
[0015]
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0016]
<Example 1: Detection of disconnection between motor and control unit>
FIG. 1 is a block diagram showing the present embodiment corresponding to FIG. 10, in which a motor drive system abnormality detecting means 300 and an integrator 301 are provided. When the connection between the motor 20 and the control unit 30 is broken, no current flows through the motor 20, so that the motor current detection value i becomes zero with respect to the motor current command value I. Since feedback control is performed on the motor current, when the detected motor current value i becomes zero, the motor terminal voltage Vm (or the PWM duty ratio) suddenly reaches a maximum value. The value of the motor terminal voltage Vm (or the PWM duty) in consideration of the fluctuation of the battery voltage is integrated by providing the integrator 301. FIG. 2 shows a connection relation for measuring the motor terminal voltage Vm in correspondence with FIG. 9, so that voltages Vm1 and Vm2 across the motor 20 connected to a predetermined voltage Vig via the resistors R3 and R4 are obtained. It has become. The integrator 301 integrates the input values during a predetermined time, and always replaces the latest input value with the input value after the predetermined time has elapsed. Then, a normal range of the integrated value of the motor terminal voltage Vm in consideration of the variation of the battery voltage with respect to the motor current command value I is determined in advance, and the integrated value of the motor terminal voltage Vm exceeding the range is determined. If it is detected for a predetermined time or more, the motor drive system or more detection means 300 determines that the connection between the motor 20 and the control unit 30 has been disconnected, and outputs an abnormal signal AL. Thus, the motor drive circuit 37 stops driving the motor 20.
[0017]
FIG. 3 shows an operation example of the motor drive system abnormality detecting means 300. First, the motor current command value I is read (step S1), and the motor terminal voltages Vm1 and Vm2 from both ends of the motor 20 shown in FIG. (Step S2). Then, the motor terminal voltage Vm is calculated according to the following equation (1).
[0018]
(Equation 1)
Vm = | Vm1-Vm2 |
Next, the obtained motor terminal voltage Vm is input to the integrator 301 (step S4), the integrated output α of the integrator 301 is read (step S5), and thereafter, abnormality detection of the integrated value with respect to the motor current command value I is performed. The value α _err is read (step S6).
[0019]
Upon reading the abnormality detection value α _err , the motor drive system abnormality detection means 300 compares the integrated output α from the integrator 301 with the following equation 2 (step S10).
[0020]
(Equation 2)
α ≧ α _err
If the formula 2 is not satisfied, the process is normal because it is normal, and the process returns to the step S1. If the formula 2 is satisfied, it is determined whether or not a predetermined time (for example, several hundred milliseconds) has elapsed (step S11). If the predetermined time has not elapsed, the process returns to step S1 to repeat the above operation. When the predetermined time has elapsed, it is determined that the motor drive system is out of order (step S12), and an abnormal signal AL is input to the motor drive circuit 37 to stop driving the motor 20 (step S13).
[0021]
<Example 2: Detection of motor ground fault>
FIG. 4 is a block diagram showing the present embodiment corresponding to FIG. 10, and includes a motor drive system abnormality detecting means 310 that uses the motor current command value I and the output of the integration calculator 36 as input signals. When the motor wire is grounded on the motor cold side, a current flows through the motor 20 due to the short-circuit portion, so that the motor current detection value i becomes zero with respect to the motor current command value I. Since feedback control is performed on the motor current, the output of the integration calculator 36 rapidly increases and reaches a maximum value. Therefore, a normal range of the output of the integration calculator 36 is predetermined for the motor current command value I, and when an output of the integrator exceeding the range is detected for a predetermined time or more, the motor drive system abnormality is detected. The detecting means 300 outputs an abnormal signal AL upon judging that the motor line is grounded. Thus, the motor drive circuit 37 stops driving the motor 20.
[0022]
<Embodiment 3: Detection of disconnection between motor and control unit>
FIG. 5 is a block diagram showing the present embodiment corresponding to FIG. 10, and is provided with a motor drive system abnormality detecting means 320 that uses the output of the integration calculator 36 and the motor current detection value i as input signals.
[0023]
For example, as shown in FIG. 6, when the motor current command value I is inputted in a step-like manner, the motor current detection value i gradually increases, and the current feedback is performed so that the motor current detection value i finally becomes equal to the motor current command value I. . An amount proportional to the deviation between the motor current command value I during transient and the motor current detection value i is accumulated in the integration calculator 36 in this current loop, and since the deviation is zero in a steady state, the integrator output is Keep a constant value. When a disconnection occurs between the motor 20 and the control unit 30 or when a failure occurs in the motor current detection circuit 38, the motor current detection value i becomes zero, and the deviation between the motor current command value I and the motor current detection value i becomes longer. Since the deviation itself is large even after the lapse of time, and the deviation itself is large, the accumulation amount of the integral computing unit 36 rapidly increases with time, and the integral computing unit 36 is saturated in a short time. Therefore, a normal range of the output of the integration calculator 36 is determined in advance for the motor current detection value i, and when an output of the integration calculator 36 exceeding the range is detected for a predetermined time or more, the motor drive is stopped. The system abnormality detecting means 320 outputs an abnormality signal AL upon determining that the connection between the motor 20 and the control unit 30 has been disconnected. Thus, the motor drive circuit 37 stops driving the motor 20.
[0024]
【The invention's effect】
As described above, according to the control device for the electric power steering device of the present invention, since the disconnection between the motor and the control unit is detected and the motor ground fault is detected, the failure of the motor drive system can be reliably detected. it can.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a first embodiment of the present invention.
FIG. 2 is a connection diagram illustrating a measurement system of a voltage between motor terminals.
FIG. 3 is an abnormality detection flowchart showing an operation example of the first embodiment.
FIG. 4 is a block diagram showing a second embodiment of the present invention.
FIG. 5 is a block diagram showing a third embodiment of the present invention.
FIG. 6 is a characteristic diagram showing an operation example of the third embodiment of the present invention.
FIG. 7 is a block diagram illustrating an example of an electric power steering device.
FIG. 8 is a block diagram showing a general internal configuration of a control unit.
FIG. 9 is a connection diagram illustrating an example of a motor drive circuit.
FIG. 10 is a block diagram showing an example of a conventional apparatus.
[Explanation of symbols]
REFERENCE SIGNS LIST 1 steering handle 5 pinion rack mechanism 10 torque sensor 12 vehicle speed sensor 20 motor 30 control unit 31 phase compensator 37 motor drive circuit 38 motor current detection circuit 39 abnormality detection units 300, 310, 320 motor drive system abnormality detection means

Claims (2)

A torque sensor for detecting a steering torque of a steering wheel, a motor for urging an auxiliary load on a steering shaft provided integrally with the steering wheel, and a control unit for driving the motor according to the magnitude of the steering torque. In the control device of the electric power steering device, when the motor current detection value is equal to or less than a predetermined value and the state in which the integrated value of the motor terminal voltage or the PWM duty ratio is equal to or more than a predetermined value continues for a predetermined time, the motor driving system A control device for an electric power steering device, wherein the control unit determines that a failure has occurred and stops driving the motor. A torque sensor for detecting a steering torque of a steering wheel, a motor for urging an auxiliary load on a steering shaft provided integrally with the steering wheel, and a control unit for driving the motor according to the magnitude of the steering torque. In the control device of the electric power steering apparatus, when the motor current detection value is equal to or less than a predetermined value and the output of the integrator of the control unit is equal to or more than a predetermined value for a predetermined time, it is determined that the motor drive system has failed. A control device for the electric power steering device, wherein the driving of the motor is stopped.

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